(3) Effect of death on enzymes. In the living, healthy animal, enzymes are
held in proper balance by the processes of body maintenance. At death, this control
ceases and the enzymes are free to attack any substance that they are capable of
breaking down. Digestive enzymes are free to attack the intestinal wall and escape to
the abdominal cavity where their action is continued. Tissue enzymes, normally found
throughout the body, are freed to act on surrounding tissue. The chief effect of enzyme
action is the softening of fish flesh. After death, effective preservation methods such as
the use of heat, refrigeration, or dehydration must be used to control the rate and extent
of enzyme action.
(4) Delay of autolytic action. Autolytic action shortens the duration of rigor
mortis. However, autolytic action may be delayed by rapid cleaning and cooling of the
fish. For all practical purposes, autolysis is stopped when fish are frozen.
d. Putrefaction. Putrefaction is the third chemical change and is evidenced by
identifiable odors of deterioration. These odors range from mild to those that are
obnoxious. When these odors are present, the fish are considered to be unacceptable
for human consumption.
(1) Enzyme action. Bacteria causes spoilage by the enzymes they secrete.
The unicellular bacteria can only live on food in a liquid state which can be absorbed
through their cell membrane. Before bacteria can multiply on a solid food, they must
secrete enzymes to break down the solids into simpler substances. Bitter flavors and
unpleasant odors, characteristic of "spoiled" food, are derived from the breakdown
substance not absorbed by the bacteria.
(2) Rapid growth of bacteria. Bacteria are present almost everywhere,
including the water in which fish live. They are found in large numbers in the body
slime, on the gills, and in the digestive tract. As long as the fish is healthy, they have
little, if any, effect on the host. At death, however, the fish cease to maintain barriers to
bacterial assault, and with the softening of the flesh by autolysis, the growth and spread
of bacteria is facilitated.
(3) Factors related to bacterial deterioration. The rate and extent of
bacterial deterioration is controlled by the following factors.
(a) The initial load of bacteria on the fish when taken from the water. A
thorough washing of the fish to remove the slime eliminates large quantities of bacteria.
Evisceration and removal of the gills aboard the ship remove large numbers of
organisms before they can multiply.
(b) The temperature of the fish. Because bacteria multiply more rapidly
at warm temperatures, fish caught in warm waters are more subject to spoilage than
those caught in colder waters. Immediate icing aboard ship and care in packing the
body cavity with ice hastens chilling. Freezing checks bacterial action as long as the
product remains frozen.